This invention relates to thermally Stable phosphorothionates from cashew nut shell liquid for use as thermally stable, antioxidant, antiwear and extreme pressure additives in a lubricant composition. The said additive for use in a lubricant controls wear on metal parts and enhances its load carrying properties.
Lubrication involves the process of friction reduction, accomplished by maintaining a film of a lubricant between two surfaces which are moving with respect to each other. The lubricant prevents contact of the moving surfaces, thus greatly lowering the coefficient of friction. Since lubricants for different uses operate under different conditions, numerous additives have been developed to establish or enhance various properties of lubricants. Representative types of additives which are used include viscosity improvers, detergents, dispersants, antioxidants, extreme pressure additives, corrosion inhibitors and others. Frequently, combinations of additives are required.
Of particular importance in many applications are antiwear agents, many of which function by a process of interaction with the surfaces, thereby providing a chemical film which prevents metal-to-metal contact under high load conditions. Wear inhibitors which are useful under extremely high load conditions are frequently called xe2x80x9cextreme pressure agentsxe2x80x9d. These extreme pressure agents are frequently selected from the following chemical types: zinc organodithiophosphates; sulfurized olefins, chlorinated waxes; amine salts of phosphate esters; phosphites; and others. Certain of these materials, however, must be used judiciously in certain applications due to their property of accelerating corrosion of metal parts, such as bearings. In addition, some applications require very low concentrations of certain elements, such as phosphorus, which restricts the utility of otherwise quite useful extreme pressure agents.
An exhaustive literature review was conducted to examine the types of chemistries in use as antiwear and EP additives. Example of antiwear and extreme pressure additives are: sulfur-and/or phosphorous-and/or halogen-containing compounds, such as sulfurized olefins and vegetable oils, zinc dialkyldithiophosphates, tritolyl phosphate, tricresyl phosphate, chlorinated paraffins, alkyl and aryl di- and trisulfides, amine salts of mono- and dialkyl phosphates, amine salts of methylphosphonic acid, diethanolaminomethyl tolyltriazole, di(2-ethylhexyl)-aminomethyltolyltriazole, derivatives of 2,5-dimercapto-1,3,4-thiadiazole, triphenylthiophosphate (triphenyl phosphorothioate), diphenylmonononylphenyl phosphorothioate, isobutylphenyl diphenyl phosphorothioate, derivatives of 2-mercaptobenzothiazole and ethoxycarbonyl 5-octyldithiocarbamate.
The object of the present invention is to provide for a thermally stable, antioxidant, antiwear and extreme pressure lubricant additive, derived from CNSL, a renewable and biodegradable product from vegetable sources and often available at very low price, which would amount to substantial overall reduction in the cost of quality, energy efficient lubricant/fuel formulations.
Another object of the present invention is to provide for a lubricant composition and more particularly, to lubricant compositions comprising oils of lubricating viscosity or greases thereof containing a minor thermally stable antioxidant, antiwear and extreme pressure additive derived from cashew nut shell liquid.
Cashew nut shell liquid (CNSL) occurs as a reddish brown viscous liquid in the soft honeycomb structure of the shell of cashewnut, a plantation product obtained from the cashew tree, Anacardium Occidentale L. Native to Brazil, the tree grows in the coastal areas of Asia and Africa. Cashewnut attached to cashew apple is grey colored, kidney shaped and 2.5-4 cm long. The shell is about 0.3 cm thick, having a soft leathery outer skin and a thin hard inner skin. Between these skins is the honeycomb structure containing the phenolic material popularly called CNSL. Inside the shell is the kernel wrapped in a thin brown skin, known as the testa.
The nut thus consists of the kernel (20-25%), the shell liquid (20-25%) and the testa (2%), the rest being the shell. CNSL, extracted with low boiling petroleum ether, contains about 90% anacardic acid and about 10% cardol. CNSL, on distillation, gives the pale yellow phenolic derivatives, which are a mixture of biodegradable unsaturated m-alkylphenols, including cardanol. Catalytic hydrogenation of these phenols gives a white waxy material, predominantly rich in tetrahydroanacardol.
CNSL and its derivatives have been known for producing high temperature phenolic resins and friction elements, as exemplified in U.S. Pat. Nos. 4,395,498 and 5,218,038. Friction lining production from CNSL is also reported in U.S. Pat. No. 5,433,774. Likewise, it is also known to form different types of friction materials, mainly for use in brake lining system of automobiles and coating resins from CNSL. However, the first application of CNSL in making lubricating oil additives was disclosed by us in U.S. Pat. Nos. 5,916,850 and 5,910,468.
Our U.S. Pat. No. 5,916,850 described development of multifunctional additives from cashew nut shell liquid or from saturated alkylphenols derived from cashew nut shell liquid. The patent relates to a process for preparing tri (alkylaryl) phosphorodithioate. The products of this invention were found to have better antifriction, extreme pressure and antiwear properties. In another U.S. Pat. No. 5,910,468, cashew nut shell liquid has been exploited for developing overbased calcium phenate detergents as additives for lubricant formulations. In another U.S. Pat. No. 6,339,052, additives derived from cashew nut shell liquid were exploited in lubricant compositions for internal combustion engines.
To achieve the said objects, the present invention provides for CNSL phosphorothionates. It also provides for a process for the preparation of CNSL phosphorothionates for use as an thermally stable, antioxidant, antiwear and extreme pressure additive in a lubricant composition, comprising the steps of hydrogenating distilled technical cashew nut shell liquid (CNSL) with a catalyst as herein described to fully hydrogenate the olefinic chain and reacting said cashew nut shell liquid with phosphorus trihalides and sulphur, the reaction being carried out at a temperature ranging from 20 to 220xc2x0 C.
The materials of the present invention are useful as additives for lubricants in which they can function primarily as thermally stable antiwear, antiscuff, and/or extreme pressure agents. They may be employed in a variety of lubricants based on diverse oils of lubricating viscosity, including natural and synthetic lubricating oils and mixtures thereof. These lubricants include crankcase lubricating oils for spark-ignited and compression-ignited internal combustion engines, including automobile and truck engines, two-cycle engines, aviation piston engines, marine and railroad diesel engines, and the like. They can also be used in gas engines, stationary power engines and turbines and the like. Automatic or manual transmission fluids, transaxle lubricants, gear lubricants, including open and enclosed gear lubricants, tractor lubricants, metal-working lubricants, hydraulic fluids and other lubricating oil and grease compositions can also benefit from the incorporation therein of the compositions of the present invention. They may also be used as wirerope, walking cam, way, rock drill, chain and conveyor belt, worm gear, bearing, and rail and flange lubricants.
The compounds of the invention can be incorporated into lubricating oils and power transmitting oils as an antiwear additive in an amount from between about 0.01 to 5 wt. %, preferably from between about 0.1 to 1.5 wt. %, most preferably from between about 0.2 to 1.0 wt. %. The oleaginous materials may be formulated to contain other additives such as viscosity modifiers, auxiliary antioxidants, friction modifiers, dispersants, antifoaming agents, auxiliary antiwear agents, pour point depressants, detergents, rust inhibitors and the like.
Compositions containing the above additives are typically blended into base oils in amounts sufficient to provide their normal attendant function. Representative examples of amounts in which these additives are conventionally to lubricating oils are as follows:
The additives can be incorporated into the lubricating oil in any convenient manner. Thus, they can be added directly to the oil by dispersing or dissolving same in the oil. Such blending can be performed at room temperature or at elevated temperatures. Alternatively, the additives may be first formed into concentrates, which are subsequently blended with the oil. The final formulations may typically contain from between about 2 wt. % to 20 wt. % of additives.
Suitable dispersants include hydrocarbyl succinimides, hydrocarbyl succinamides, mixed ester/amides of hydrocarbyl substituted succinic acid, hydroxyesters of hydrocarbyl-substituted succinic acid, amides of aromatic acids and Mannich condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines. Mixtures of such dispersants can also be employed.
The preferred dispersant for use in combination with the CNSL phosphorothionate additives of the present invention are alkenyl succinimides. These acyclic hydrocarbyl substituted succinimides are formed with various amines, polyamines and amine derivatives, and are well known to those of ordinary skill in the art. An example of a particularly suitable dispersant is the polyisobutenyl succinimide reaction product of polyisobutylene succinic anhydride, wherein the polyisobutene moiety preferably has a number average molecular weight in the range from between about 500 to 5000, preferably from between about 800 to 2500 and an alkylene polyamine such as triethylene tetramine or tetraethylene pentamine or mixtures of polyamines containing 3 to 12 nitrogen atoms per molecule, known in the art as PAM. The use of alkenyl succinimides that have been treated with an inorganic acid of phosphorus (or an anhydride thereof) and a boronating agent are also suitable for use in combination with the compounds of the invention and are more compatible with elastomeric seals made from such substances as fluoroelastomers and silicon elastomers.
Suitable antioxidants for use in combination with the additives of the present invention include amine-type and phenolic antioxidants. Examples of amine-type antioxidants include phenyl alpha napthylamine, phenyl beta naphthalyamine and bis- alkylated diphenyl amines (e.g., p,pxe2x80x2-bis(alkylphenyl)-amines wherein the alkyl groups each contain from 8 to 12 carbon atoms). Phenolic antioxidants include sterically hindered phenols (e.g., 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert-butylphenol) and bis-phenols (e.g., 4,4xe2x80x3-methylenebis(2,6-di-tert-butylphenol). Phosphorous compounds, such as ZDDP, or phosphites are also commonly added to automatic transmission fluids (ATF) and passenger car motor oils (PCMO) as antioxidants. In addition to providing antiwear properties, the compounds of the present invention provide antioxidant credits to lubricating compositions, allowing for the formulation of lubricating compositions with a reduced amount, or no amount, of dedicated antioxidant additive.
Suitable friction modifiers are molecules having a polar head group and an oleophilic tail group. The polar head groups cause the molecule to be adsorbed onto the friction surface. These groups can be, but are not limited to, amines, mono and diethoxylated amines, carboxylic acids, amides, imides, alcohols, phenols, thiols, sulfonic acids, phosphites, phosphates, esters and combinations thereof. The oleophilic groups are typically alkyl groups, normally linear alkyl groups. These alkyl groups range in carbon number from between about C.sub.8 to C.sub.30, preferably from C.sub.12 to C.sub.20. They may be saturated or unsaturated, and may contain hetero atoms such as nitrogen or sulfur providing that the hetero atoms do not adversely affect the ability of the molecule to function as a friction modifier.
Examples of friction modifiers suitable for use with the antiwear additives of the invention include oleamide, tallow amine, diethoxylated tallow amine, N,N-bis(2-hydroxyethyl)-octadecyl amine, N,N-bis(2-hydroxyethyl)-stearyloxypropylamine, oleic acid, N,N-hydroxyethyl,N-(Nxe2x80x2, Nxe2x80x2-bis(2-hydroxyethyl)ethylamine)-stearylamine and the diamide produced from isostearic acid and tetraethylene pentamine, molybdenum dithiocarbamates and molybdenum dithiophosphates.
Suitable compounds for use as viscosity modifiers are generally high molecular weight hydrocarbon polymers, including polyesters. Oil soluble viscosity modifying polymers generally have weight average molecular weights from about 10,000 to 1,000,000, preferably from about 20,000 to 500,000, as determined by gel permeation chromatography or light scattering methods.
Representative examples of suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene and higher alpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylate copolymers, copolymers of unsaturated dicarboxylic acid and vinyl compound, inter polymers of styrene and acrylic esters, and partially hydrogenated copolymers of styrene/isoprene, styrene/butadiene and isoprene/butadiene, as well as partially hydrogenated homopolymers of butadiene and isoprene and isoprene/divinylbenzene.
Lubricating oils and power transmission oils incorporating the antiwear additives of the invention may also contain rust inhibitors such as nonionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, phenoxyacetic acids and anionic alkyl sulfonic acids, as well as corrosion inhibitors, such as thiadiazole polysulfides containing from between about 5 to 50 carbon atoms, their derivatives and polymers thereof; derivatives of 1,3,4-thiadiazoles; and thio and polythio sulfenamides of thiadiazoles. Such oils may also contain an antifoamant, including polyacrylate-type antifoamants, polysiloxane-type antifoamants and fluorosilicone-type antifoamants, and detergents, such as overbased and neutral calcium sulfonate, calcium phenate, magnesium sulfonate and magnesium phenate.
Generally speaking, the process of manufacturing the additives in accordance with this invention may be carried out as follows:
Specifically, cashew nut shell liquid is distilled at reduced pressure to yield a mixture of biodegradable olefinic phenols. The components of CNSL contain a phenolic hydroxyl group and an C15H31xe2x88x92n unsaturated side chain, where n=0,2,4 or 6. Such a mixture is converted to their saturated C15 phenol derivatives by catalytic reduction in the presence of a palladium or platinum or nickel hydrogenation catalyst. The alkyl phenol is treated with phosphorus trihalides and sulphur in the presence of a solvent. After the completion of the reaction, the solvent is removed and product extracted with another organic solvent to yield the desired CNSL phosphorothionate derivatives.
Triaryl thiophosphates are known plasticizing and flame retardant agents for polymers. However, symmetrical triaryl thiophosphates e.g triphenyl phosphate, are crystalline solids. This detracts from their use as plasticizers as they have a tendency to crystallize and bloom to the surface of the plasticized composition. As solids, these compounds are difficult to process and handle. They also have a disagreeable H2S odor.
The composition of the invention can also be prepared by forming a mixture of cashew nut shell liquid and phenol or substituted phenol. This cardanol mixture is then reacted with a phosphorous trihalide, e.g chloride or bromide, in an amount sufficient to completely substitute to halide cites though more or less can be used. Generally 3.0-3.5 molecular equivalents (xcx9c5-15% excess) of the phenols as per molecular equivalent of phosphorous trihalide is used. The reaction is carried out by heating mixture of reactants to a temperature at which hydrogen halide is involved, i.e. between about 30xc2x0 C. and about 200xc2x0 C. If desired a nitrogen sparge and a catalyst such as a metal or metallic chloride catalyst can be employed. Any excess phenol can be stripped under vacuum. The triaryl phosphite/mixed triaryl phosphite product can then be reacted directly with sulphur to form the triaryl thiophosphate/ mixed triaryl thiophosphate final product. The reaction with the sulphur is generally carried out by heating the reactants with an amount of sulphur, preferably powdered sulphur, equimolar to the phosphite at temperature ranging from about 140xc2x0 C. to about 250xc2x0 C. for a sufficient time to accomplish the reaction depending on temp and reactants, e.g. for about 1-3 hours, to yield CNSL phosphorothionates.
The compounds of the invention can also be prepared by reacting thiophosphoryl chloride with the cardanol and mixed phenol blend. The sulfurization step can be avoided though the other steps apply. When using thiophosphoryl chloride it is again important to the operation of the invention that any distillation be prior to the base washing and mild drying.